Internet of Things (IOT) is “the Internet of connected things”, and it extends a user end of the Internet to everything for information exchange and communication. Such a communication manner is also referred to as machine type communication (MTC), and a communications node is referred to as an MTC terminal. A typical application of Internet of Things includes smart metering, smart household, and the like. Because Internet of Things needs to be applied to multiple scenarios, such as an outdoor, indoor, or underground environment, many special requirements are imposed on design of Internet of Things.
First, Internet of Things needs to have strong coverage performance. Many MTC devices such as an electricity meter or a water meter are in a relatively poor coverage environment. They are usually installed in a place with an extremely weak wireless network signal, such as an indoor corner or even a basement, and in this case, a coverage enhancement technology is required to implement coverage of Internet of Things.
Second, Internet of Things needs to support a large quantity of low-rate devices. A quantity of MTC devices is far greater than that of devices used in communication between persons. However, a data packet transmitted by the MTC device is small and is delay-insensitive.
Third, a device of Internet of Things needs to be cost-effective. In many MTC applications, it is required to obtain and use MTC devices at low costs, so that the MTC devices can be deployed on a large scale.
Fourth, a device of Internet of Things needs to feature low energy consumption. In most cases, an MTC device is battery-powered. However, in many cases, an MTC device is required to operate properly for more than a decade without a battery replacement, and this requires that the MTC device can operate with extremely low energy consumption.
So far, an expected objective of low costs, wide coverage, and low energy consumption still cannot be achieved. To satisfy the foregoing special requirements, in a recent project of Narrowband Internet of Things (NB-IOT), three deployment modes are defined:
(1) Standalone operation: That is, a standalone frequency band is used, for example, one or more carriers of a Global system for mobile communications (GSM) network is used.
(2) In-band operation: One or more physical resource blocks (PRB) in a Long Term Evolution (LTE) carrier are used.
(3) Guard band operation: An unused resource block in an LTE carrier guard band is used.
In the foregoing three modes, carrier center frequency locations for deploying NB-IoT may be different, and may be inconsistent with an original carrier center frequency defined based on a 100 kHz raster in LTE. However, when accessing a network, a terminal does not know where an NB-IoT system is deployed, let alone which specific deployment mode is used. Therefore, because a carrier center location of NB-IoT in the in-band operation and the guard band operation is inconsistent with an original carrier center location in LTE, in this case, if the terminal continues to search for an NB-IoT cell by using the carrier center defined in LTE, the terminal possibly cannot find a cell, and frequent cell searching consumes much power and reduces a battery life of an NB-IoT terminal.